516 ME. A. D. MICHAEL ON THE 



organs, and I do not know any instance of their being glandular ; the mucous glands of 

 Bdella are some of the largest organs in the body. The histology of the mucous glands 

 is essentially that of the accessory glands of the male genital system in many other 

 Acari, e. g. Gamasus, the large thick-walled cells immediately striking the observer 

 as similar ; but the accessory glands of other Acari are always separate organs, ending 

 lilindly and discharging by ducts ; and the discharge of spermatozoa through such glands 

 seems 2^rr>na fcfcie to be improbable. I have been very unwilling to accept it as the true 

 explanation ; it has even struck me whether it were possible that at some time of year 

 which I have missed, or ixnder some circumstances, the testicular bridge does com- 

 municate with the penial canal, and whether in that case it might be possible that the 

 mucous gland not only discharged its principal contents, as it certainly does, through 

 the antechamber into the penial canal, but also discharged some portion through the 

 narrow constricted aperture into the common duct and bridge, where it served to nourish 

 the spermatozoa, which appear so much better nourished in this place than anywhere 

 else. I have not, however, been able to discover any sufficient evidence in favour of such 

 a theory, and it is not by any means a theory to be accepted without evidence, as a 

 gland discharging at both ends to different organs is not a thing which could be 

 anticipated. 



The head of the penial canal is enveloped by a thick cap of muscles spanning it in all 

 directions ; these doubtless are the ejaculatory muscles, and, probably, serve also to 

 extrude the invaginated parts of the canal. What can be the office of the embedding- 

 sac in £. Basteri, and what is the necessity for the number, variety, and immense size of 

 the accessory glands in all species of Bdella it is very difficult to understand. 



The Female. (Figs. 24, 25, 43, 44.) 



In marked contrast to the extreme complication of the generative organs of the male- 

 Bdella, those of the female are particularly simple, and we do not find a single accessory 

 gland present to take the place of the numerous organs of that nature which are present 

 in the male. 



Practically it is only in young specimens that these organs can be studied ; when the 

 eggs are matured they fill the abdomen so miich that they push everything else out of 

 position ; and if the genital organs be dissected out they are a mere lump of eggs which 

 hide everything, and have distended some parts out of all shape, while sections at this 

 time do not reveal much more. 



The organs of the female consist of: (1) the ovary ; (2) the oviduct; (3) the recep- 

 taculum seminis ; (4) the external labia. 



The Ovary (figs. 24, 25). — This organ is a considerable variation from all homologous 

 organs hitherto described in the Trombidlnm-gvow]) of Acarina (vide Heukin (6), Michael 

 (14), Schaub (18)) ; in all these recorded instances the ovary has been almost ring-shaped 

 and flattened, the paired oviducts completing the ring. In Bdella the ovary is a mere 

 crescentic lump, which in the virgin female is quite small, but of course provided 

 with ovarian ova ; the crescent is a short and slightly ciu'ved one (fig. 25, ov). As the 



